This invention generally relates to an apparatus and process for simultaneously manipulating probes within conduits, and is specifically concerned with a device for simultaneously oscillating a plurality of heater probes within a plurality of heat exchanger tubes mounted in the tubesheet of a nuclear steam generator in order to thermally stress relieve these tubes.
New processes for thermally relieving the tensile stresses which may occur in the support plate regions of the heat exchanger tubes of a nuclear steam generator have recently created a need for a device that is capable of moving such heater probes along an oscillatory path within such tubes. Specifically, in the heat-treating process disclosed and claimed in copending U.S. patent application Ser. No. 069,721 filed June 6, 1987, by Wenche Cheng and assigned to the Westinghouse Electric Corporation, a heater probe in the form of a 1,000 watt tungsten halogen quartz lamp is inserted into the open end of a tube and oscillated in a portion of a heat exchanger tube which is circumscribed by a support plate in order to relieve the tensile stresses which are created in the annular space between the plate and the tube by the accumulation of sludge therebetween. The principal purpose of this process is to uniformly heat the walls of a heat exchanger tube in the support plate region to a temperature of between 1350 to 1450 degrees F. for a time period of approximately 4 to 6 minutes. As is specifically pointed out in the specification of this copending patent application (which is incorporated by reference into the instant specification), the heat sink properties of the support plate that surrounds the heat exchanger tube create a formidable obstacle to the attainment of a uniform heat gradient in this particular region of the heat exchanger tube. Experimental attempts Lo attain such a uniform temperature gradient through the use of a statically held heater probe had failed, with the center portion of the tube section (which contacts the plate) being underheated, and the end portions of the tube section being overheated. However, the inventor of copending U.S. patent application Ser. No. 069,721 overcame this problem by a process wherein the heat probe used to heat the section of the tube is oscillated such that the dwell time at the midpoint of the oscillation cycle (closest to the support plate) is twice as great as the dwell time at the end points of the oscillation cycle.
Initially, the aforementioned process was implemented by the manual manipulation of a push-cable connected to the heater probe. Later, a device was developed by the Westinghouse Electric Company that was capable of manipulating a single probe in a single tube. This device generally comprised a frame with a bladder-type gripper capable of gripping the push-cable connected to a probe. The gripper was in turn threadedly engaged to a leadscrew which was turned by a reversible D.C. motor. The frame further included a "pop-up" cylinder capable of temporarily raising the heater probe up a few inches so that an optical fiber connected to the probe could conduct the incandescent glow of the heated tube section back to a two-color pyrometer in order to obtain a temperature reading of the tube. The entire device was coupled to a robotic arm. While such a device has been shown to effectively implement the new heat treating process disclosed in copending patent application Ser. No. 069,721, the Applicant has observed several shortcomings associated with such a device, the most serious being its ability to heat-treat only one tube at a time. Since it may be necessary to heat-treat hundreds of heat exchanger tubes to complete the servicing of a single generator, the time required to complete the servicing could be lengthy. Such a lengthy servicing time could result in an increased downtime for the generator, which costs over $100,000.00 per day in lost revenues, and could also increase the amount of exposure of the maintenance personnel to potentially harmful radiation. Still other shortcomings of this single-tube device stem from its size and bulk, which requires the use of a robotic arm to support it in place after the device is positioned adjacent to the tube to be serviced, thus tying up the use of such an arm during the entire procedure. This is a significant drawback as there is only room for one such arm in the channel head of the generator to perform all the needed maintenance procedures.
Clearly, there is a need for a device that is capable of accurately positioning and simultaneously oscillating a plurality of such heater probes within the heat exchanger tubes of a steam generator in order to expedite the maintenance procedure. It would be desirable if such a device were capable of supporting itself once it was delivered to a desired position within the tubesheet of the steam generator so that the robotic arm used to deliver the device could be used for other purposes while the heat treatment of the tubes was being carried out. Finally, such a device should be compact and lightweight enough to be accurately held and delivered by a relatively inexpensive robotic arm, and capable of servicing both the peripherally and the centrally located tubes in the tubesheet without mechanical interference with any part of the channel head of the steam generator.